A golf game system of the present applicant is described in Jpn. unexamined patent publication No. 2004-85524. The golf game system includes a game apparatus and a golf club type input device, and an imaging unit including an image sensor and infrared emitting diodes is provided within a housing of the game apparatus. The infrared emitting diodes intermittently emit infrared light to a prescribed area above the imaging unit. Therefore, the image sensor intermittently picks up an image of a reflective portion attached to the golf club type input device which moves within the prescribed area. The speed of the golf club type input device which is an input to the game apparatus is calculated by processing images of the reflective portion captured by the stroboscope. In this way, input is given to a computer or a game apparatus in real time by means of the stroboscope.